macOS support

[BjarneSeger]

This change allows more people to use gitlab_trackr. Which is good.

Since we use varlink for IPC and basically nothing OS-specific in the code, the raw application should be ready to go. The most important missing piece would be the launchd config, which I currently cannot test.

[leontappe]

My macOS Features:

• Pending bookings
  • Notice network faults etc.
  • Retry logic
  • Book at original time (not the time of retry)
• Groups filter
• History
  • Combine pending local bookings and query past bookings on assigned issues
• Issue information
  • Graph status
  • Parent/Epic
  • Total tracked time
  • etc?
• Issue actions?
  • Close
  • Change status
  • Change assignment
  • obviously book time ayyylmao
• Standby/Hibernate handling

[BjarneSeger]

Gitlab does not seem to permit manually setting the time when adding it: https://docs.gitlab.com/api/issues/#add-spent-time-for-an-issue
The only available fields are duration, id, issue_iid and summary

[leontappe]

GraphQL docs say otherwise:
https://docs.gitlab.com/api/graphql/reference/#mutationtimelogcreate

Note: probably only works with Enterprise Edition

[BjarneSeger]

Should be implemented with https://github.com/BjarneSeger/gitlab_trackr/releases/tag/v0.4.0, with the exception of changing assignment / status, because that involves querying users as well (which seems a bit outside of scope for time tracking)

[BjarneSeger]

Currently still missing:

• History actually working
• (Un)Assigning yourself
• Changing the issue status Would involve having to query for all labels, which is out of scope